In 1957, Marie Tharp published an unusual map. Instead of the land, the US scientist’s map showed the floor of the Atlantic Ocean. If you haven’t seen it, or Tharp’s later maps of the other oceans, you’ve probably seen versions of them – the seabed revealed in 3D, as if all the water has been drained away, revealing mountain chains running for thousands of kilometres and valleys deeper than anything above sea level.
Given how little of the seabed had been reliably surveyed, Tharp’s maps relied heavily on creative licence, but they vividly delivered the message that the deep ocean floor is not a flat, featureless place. They also helped to make the case for the idea of continental drift.
Tharp is one of the key protagonists in Laura Trethewey’s story of the effort to chart the unmapped areas of the seabed, a place which – as the cliché goes – we know less about than the surface of the moon.
Science has moved on since Tharp’s day, though perhaps not as much as you might imagine. According to the organisation Seabed 2030, which aims to encourage ocean mapping, only a quarter of the world’s seabed has so far been mapped with an adequate degree of resolution. Given that the oceans cover more than two-thirds of the globe, that leaves plenty of work to be going on with.
In describing the effort to map the remaining 75%, Trethewey uses the tried-and-true technique of latching on to a few of the individuals involved and telling their stories. There are plenty of grizzled mariners and scientists – including a few Kiwis – but the key characters are newly graduated seafloor mapper Cassie Bongiovanni and her employer, Victor Vescovo, a mega-rich adventure addict on a quest to reach the deepest spot in each of the five oceans.
Vescovo must overcome numerous obstacles, not least of which is actually locating the deepest spot in all five oceans, which remains a challenge even now. Along the way, this mission provokes a flurry of claim and counterclaim between Vescovo and adoptive New Zealander James Cameron over whose dive to the ocean floor was deeper.
If 25% doesn’t sound like much of the ocean floor to have mapped, five years ago, reckons Seabed 2030, the proportion was only 15%. After all, as well as being very large, the sea also tends to be deep (average depth about 3.7km), frequently turbulent and a challenging environment in which to conduct any kind of scientific research.
Politics intrude, too. Some nations don’t like outsiders mapping “their” ocean floor, and political priorities often make it hard to find the resources to make maps of a place no one is likely to visit. There’s also a widespread suspicion that the 25% figure is an underestimate and would be much bigger if some nations released ocean floor surveys that remain classified for defence or economic reasons.
Inevitably, advances in technology are a big part of this story. In the early days of ocean exploration, the only way to measure the sea’s depth was to lower a weighted line all the way to the bottom. By 1960, the first expedition to reach the bottom of the Challenger Deep, the deepest known place in all the oceans, found the right spot by throwing TNT overboard and timing how long it took for the explosion’s echo to bounce back from the seabed. Today, sonar can measure depths within an accuracy of a few metres, and there are even sensors that can look beneath the seabed, hunting for buried artefacts.
There are also now submersibles that can reach the bottom of the deepest ocean – popular among super-rich men, and one of which, the Titan, tragically imploded last June. Now, autonomous mapping drones – small unmanned ships – wander the ocean, constantly making measurements.
When surveys do find undersea features – canyons, ridges, seamounts, vents, fracture zones and the rest – there’s even an international bureaucracy that earnestly decides on an official name for each discovery (no naming things after living people or commercial entities, say the rules).
New Zealand appears to be particularly active in this name-giving business. For example, 2870m below the surface of the Southern Ocean is Kūmara Hill. There’s a Kiwi Seamount, too, and – showing that scientists do have a sense of humour – a Reserve Bank, deep beneath the waves east of the South Island.
Yes, it’s an adventure story, but with enough reminders of why seabed mapping matters: whether it’s to help decide on the wisdom, or otherwise, of mining the ocean floor, looking for evidence of past civilisations, or understanding the sea’s role in controlling the climate.
